As semiconductor devices are scaled down progressively, strained source/drain (S/D) features (e.g., stressor regions) have been implemented using epitaxially grown semiconductor materials to enhance charge carrier mobility and improve device performance. For example, forming a metal-oxide-semiconductor field effect transistor (MOSFET) with stressor regions may epitaxially grow silicon (Si) to form raised S/D features for n-type devices, and epitaxially grow silicon germanium (SiGe) to form raised S/D features for p-type devices. Various techniques directed at shapes, configurations, and materials of these S/D features have been implemented to further improve transistor device performance. However, existing approaches in raised S/D formation have not been entirely satisfactory.
For example, forming raised S/D regions at an active region next to an isolation region (or structure) has been problematic. For example, trenches for growing epitaxial features at the boundary of the two regions may not have an ideal shape. Also these trenches are only partially surrounded by semiconductor material(s). As a result, epitaxial features grown from these trenches might be thinner than those grown completely within the active region. Consequently, when contact features are formed above these epitaxial features, contact landing might be slanted and contact resistance might be high. Improvements in these areas are desired.